Selective electrochemical accelerator removal

ABSTRACT

Methods and apparatus are provided for planar metal plating on a workpiece having a surface with recessed regions and exposed surface regions; comprising the steps of: causing a plating accelerator to become attached to said surface including the recessed and exposed surface regions; selectively removing the plating accelerator from the exposed surface regions without performing substantial metal plating on the surface; and after removal of plating accelerator is at least partially complete, plating metal onto the surface, whereby the plating accelerator remaining attached to the surface increases the rate of metal plating in the recessed regions relative to the rate of metal plating in the exposed surface regions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/860,787, filed Aug. 20, 2010, now U.S. Pat. No. 8,268,154, issuedSep. 18, 2012, which is a continuation of U.S. patent application Ser.No. 11/544,957, filed Oct. 5, 2006, now U.S. Pat. No. 7,799,200, issuedSep. 21, 2010 which is a continuation-in-part of U.S. patent applicationSer. No. 11/065,708, filed Feb. 23, 2005, now U.S. Pat. No. 7,531,079,issued May 12, 2009, which is a continuation-in-part of U.S. patentapplication Ser. No. 10/739,822, filed Dec. 17, 2003, now U.S. Pat. No.7,449,098, issued Nov. 11, 2008, which is a continuation-in-part of U.S.patent application Ser. No. 10/209,171, filed Jul. 29, 2002, now U.S.Pat. No. 6,756,307, issued Jun. 29, 2004. Each of these applications isincorporated herein by reference in its entirety and for all purposes.

U.S. patent application Ser. No. 11/544,957 also claims benefit of U.S.Provisional Patent Application Ser. No. 60/724,209, filed Oct. 5, 2005,which is incorporated by reference in its entirety and for all purposes.

U.S. patent application Ser. No. 11/544,957 is also acontinuation-in-part of U.S. patent application Ser. No. 10/947,085,filed Sep. 21, 2004, now U.S. Pat. No. 7,449,099, issued Nov. 11, 2008,which is a continuation-in-part of U.S. patent application Ser. No.10/824,069, filed Apr. 13, 2004, now U.S. Pat. No. 7,405,163, issuedJul. 29, 2008, which is a continuation-in-part of U.S. patentapplication Ser. No. 10/739,822, filed Dec. 17, 2003, now U.S. Pat. No.7,449,098, issued Nov. 11, 2008, which is a continuation-in-part of U.S.patent application Ser. No. 10/209,171, filed Jul. 29, 2002, now U.S.Pat. No. 6,756,307, issued Jun. 29, 2004.

Each of the applications and patents listed in this section isincorporated herein by reference in its entirety and for all purposes.

BACKGROUND

A principal objective of damascene circuit interconnect manufacture isto create metal isolated by and embedded in a dielectric media. Moderncopper electroplating for damascene processes proceeds by a “bottom up”fill mechanism that preferentially fills high aspect ratio features suchas deep trenches and vias on a wafer surface. The preferential fillingof recessed requires careful control of process conditions. Mayer etal., U.S. Pat. No. 6,946,065 entitled “Process for Electroplating Metalinto Microscopic Recess Features”, incorporated herein its entirety forall purposes, describe some of the issues one must consider inperforming filling operations. For the most part, prior processes do notpreferentially fill and planarize low aspect ratio features andtherefore they require significant excess metal deposition(“overburden”). Overburden is the additional copper deposited on thesubstrate to ensure that all low aspect ratio features are completelyfilled (essentially in an isotropic fashion) to the plane of the waferisolating dielectric surface (the “field”). Since the preferential“bottom-up fill” does not occur in low aspect ratio features, thesurface of the overburden typically follows the contours of theseunderlying wafer surface recesses over these features. In most cases,the overburden on field regions is slightly thicker than the thicknessof the damascene layer, typically on the order of 1.2 or more times thedepth of the deepest feature. For example, a damascene structure thathas 0.5 micrometers deep features will typically require an overburdenof at least approximately 0.7 to 0.8 micrometers.

The fact that the filling of low aspect ratio features is largelyisotropic leads to very little, if any, reduction in the overalltopography of the surface. The step change in the low aspect ratiofeatures is essentially identical to the initial patterned recess depthin the dielectric media. When combined with overplating or momentumplating associated with high aspect ratio feature, the net topographyvariation using current technology generally increases during theplating operation, and is approximately equal to the sum of the stepheight of the dielectric film thickness and the highest overplated highaspect ratio feature. A goal of the manufacturing steps is to eventuallyisolate the individual lines within the recesses of the devicedielectric layer. However if metal was subsequently isotropicallyremoved, then these low aspect ratio features would lose all the metalbelow the plane of the dielectric before the high aspect ratio lines andfield area metal was removed. A planarization or polishing technologythat removes metal more rapidly from raised regions than recessed regionis therefore used so that, at the end of the metal removal steps metalremains in these low aspect ratio features. Chemical mechanicalpolishing is one technology that is used to accomplish this end. But touse these polishing planarizing technologies, “overburden” is required.An desirable alternative would be to employ a process where the metal inrecessed features is deposited more rapidly than other areas.

Overburden is undesirable for a number of reasons. It requiresdeposition of excess copper that is essentially wasted. It requires anextra step of removing the overburden material. Thus, overburdenrepresents additional materials costs (excess copper deposited andremoved) as well as decreased throughput/productivity. Overburden istypically removed by a planarization technique such as chemicalmechanical polishing (CMP), electrochemical chemical polishing (eCMP) orother electropolishing techniques suited to planarize low aspect ratiofeatures. The CMP and eCMP processes are particularly expensive processand implement generally corrosive chemical and slurry formulations onlarge pads to polish the surface of the integrated circuit. Polishingcan be difficult to control and the polishing end-point can be difficultto detect. The high equipment cost, waste handling cost, and lowthroughput contribute to the overall expense of CMP and eCMP. Also, withthe introduction of porous low-k dielectrics in semiconductor devices,modification of traditional CMP and even eCMP processes will berequired, as current methods can lead to cracking and/or delamination oflow-k materials which are fragile and typically have a very lowcompression strength.

Measures must be taken to avoid metal “dishing”, dielectric/line“erosion”, and underlying topography during CMP. See, for example,“Establishing the discipline of physics-based CMP modeling, S. R.Runnels, and T. Lauren, Solid State Technology, March, 2002. Dishingoccurs on the interconnect metal primarily over larger features andcontact pad region during the later stages of copper CMP. Becauseelectroplating creates variations in thickness over the dielectric, andbecause underlying topography is transferred to higher levels throughthe dielectric from lower levels, within-die variations in the amount ofmetal thickness over the dielectric continue to always exist and persistup to the point of the first clearing of interconnect metal over thedamascene structure (barrier exposure). Because neither the metaldeposition (e.g., electroplating) nor metal removal (e.g., CMP)processes are perfectly uniform across the wafer surface, globalnon-uniformities also exist. Dishing of a feature generally occurs whenthe metal has cleared locally around the periphery of the feature butthe polishing process must be is continued over that feature to completethe process elsewhere. This “overpolishing” is needed, for example,because other areas of the surface have not reached the clearingendpoint. The pad tends to terminate and is “held up” at the featureperiphery by the barrier film (supported by the underlying dielectric).The barrier material is largely unaffected (i.e., removed at a muchslower rate) as the CMP of copper on the surface continues. The problemarises that the interconnect metal (e.g., copper) in the feature isslowly removed, preferentially within the feature, hence it becomes“dished”. It is believed desirable to ensure that all the interconnectmetal (copper) above the barrier/dielectric level is removed from thetop of the barrier/dielectric at this point in the process beforeproceeding with removing the typically conductive barrier film, sosignificant “overpolishing” is often needed and significant dishing canoccur. After interconnect (copper) removal above the field is complete,the barrier layer is exposed. If properly performed, the barrier islargely unaffected by this process. During the subsequentbarrier/dielectric step of the CMP process, one needs to avoid excessiveerosion. Erosion arises from locally varying polishing property ofdifferent area of the surface. This is believed due to the different CMPrates and mechanical “strength” of the substrate at different point onthe circuit. Varying feature density and the different mechanicalproperties of the metal and dielectric are the leading causes ofpolishing erosion. In the barrier/dielectric removal/polish CMP stepserosion can be viewed as primarily a mechanically driven process. Mosttopography has been removed at this stage. After the barrier has beenremoved and the dielectric is exposed, a goal of polishing is toeliminate dishing in the early copper CMP step without causing erosionof high-density area of lines. To eliminate the dishing, some amount ofdielectric is removed but this reduces the thickness of the copperinterconnects and increases the electrical resistance. The overallchanges in the planarity caused by dishing, erosion, and underlyingtopography can also lead to difficulties in obtaining good focus acrossthe die during subsequent lithographic steps. Also important, topographyintroduced by these effects is replicated at the next metal level,creating “underlying topography”. These areas are particularlytroublesome for CMP technology because of the competing requirements ofhaving planarization and compliance. Clearing metal by CMP from recessedareas of “underlying topography is difficult, often leaving “puddles” ofmetal. To remove these “puddles,” the CMP process is generally continuedfor a longer period of time than otherwise desirable because it cancreate excessive dishing.

While not intending to be held to any specific theoretical explanation,this background helps to explain the interrelationship between the typesof planarization phenomena often encountered (dishing, erosion, puddles)and illustrates the problems of the current art. These issues make CMPprogressively more difficult with advancing technology requiringadditional numbers of metal layers to be added to the structure.

Alternatives to CMP include electrolytic etching techniques such aselectropolishing or electroless etching. Compared to CMP, these arerelatively low cost techniques. They also provide much higher processingrates. Electropolishing is a method of polishing metal surfaces byapplying an electric current through an electrolytic bath, and removingmetal via electrolytic dissolution, the reverse of electroplating.

Although many previous approaches address the need for simpler andimproved electroplanarization in semiconductor device fabrication, theygenerally address alternative planarization techniques performed afterdeposition of an undesirably thick overburden with substantialvariations topography. Yet electroplating processes that deposit copperwith reduced overburden, reduce and/or control the variation oftopography, or improve planarity, are highly desirable.

J. Osterwald and J. Schulz-Harder (“New Theoretical Ideas about theAction of Bath additives”, Galvanotechnik, 66, 360, [1975] and “Levelingand Roughening by Inhibitors and Catalysts”, Oberflache-Surface, 17, 89,[1976]) proposed a smoothing and filling mechanism and action of astrongly surface-attached accelerating molecule that enablespreferential growth. Others demonstrated the usefulness of this conceptin interpreting, modeling and controlling preferential filling of smalldamascene features. See, for example, J. Reid and S. Mayer, in AdvanceMetalization Conference Proceedings, 1999, pg 53; A. C. West, S. Mayer,and J. Reid, Electrochem. Solid-State Lett., 4, C50, [2001]; T. P.Moffat, D. Wheeler, W. H. Huber, and D. Josell, Electrochem Solid StateLett, 4, C26, [2001]; and T. P. Moffat, D. Wheeler, and D. Josell,Electrochemical Society Interface, pg 46, Winter 2004.

Another class of methods useful in overburden reduction andplanarization is referred to as “brush plating” or “planar plating”.These methods generally employ a brush that acts on the surface toachieve smoother deposits during the plating process. So-calledbottom-up fill (also referred to as “superfilling”) methods are nowcommonly used to fill high aspect ratio (i.e., deeper than wide) recessfeatures, though a geometric acceleration concentration mechanismsimilar to that proposed by Ostwald et. al. and later made practical.However, the physical and geometrical limitations of these processes,mean that they are not capable of filling low aspect ratio featuresSince both high and low aspect ratio features can exist on everydamascene integrated circuit interconnect level, there is interest inany potentially low cost “planar plating” method. Various planar platingmethods that attempt to modify the otherwise conformal plating behaviorover recessed low aspect ratio region by modifying the plating method(bath additives, transport properties, field effects, etc.) have beenreported.

Schwartz (U.S. Pat. Nos. 3,183,176, 3,313,715 and 3,939,134) describes amethod and apparatus for brush planar electroplating for preparingsmooth electrodeposits, diminishing surface roughness and preferentiallyfilling recessed small crevices. Macula et al. (U.S. Pat. No. 3,751,343)also describe a brush plating apparatus and process where electrolyte isheld in and simultaneously moves through a rubbing surface element withelectrolytic plating with an orbital rubbing like motion. Eisner (U.S.Pat. Nos. 3,619,383 and 3,749,652) describes an apparatus and method ofbrush plating which uses simultaneous abrasion of the surface to reduceroughness and accumulation of unwanted metal deposition.

The following documents are incorporated herein by reference in theirentireties and for all purposes: Controlini and Mayer (U.S. Pat. No.5,486,234); Controlini and Mayer (U.S. Pat. No. 6,315,883); Controliniet al. (U.S. Pat. No. 6,709,565); Koos et al., U.S. patent applicationSer. No. 10/690,084, entitled “Method for Fabrication of SemiconductorInterconnect Structures with Reduce Capacitance, Leakage Current andImproved Breakdown Voltage, filed Oct. 20, 2003; U.S. Pat. No.6,176,992; Reid (U.S. Pat. No. 6,024,857); Bulent et al. (U.S. Pat. No.6,534,116); U.S. patent application Ser. No. 11/739,822; Reid (U.S. Pat.No. 6,653,226); and International Patent Application No. WO 2005/042810entitled “Membrane Mediated Electropolishing” in the names of Mazur etal.

SUMMARY OF THE DISCLOSURE

Aspects of the present invention relate to methods of preferentiallyfilling by electroplating features that are recessed from the generalplane of a workpiece. Aspects of the invention relate to 1) a processfor improving the filling high aspect ratio (features deeper than wide)recess features, 2) the reduction of excess electroplating thicknesscommonly observed during copper electrodeposition over high aspect ratiofeature (a “mound” or “bump” or excessive metal often found afterfilling high aspect ratio features, sometimes called “momentum” or“overplating”), and 3) the preferential filling with metal (referred tohereafter as “bottom-up” filling or selective accelerated plating) inrecessed area of a surface of low aspect ratio damascene features(features much wider than deep). The invention is thus applicable, forexample, to the manufacture of integrated circuit or other electronicdevices. Aspects of the invention further relate to hardware forperforming and controlling these processes, reducing the extent ofoverplating, providing selective accelerated plating and preferentiallyfilling high and low aspect ratio damascene features. In addition, theinvention relates to removal of excess metal, specifically the metalfrom the general planar surface of a workpiece. In certain embodiments,each of these deposition and removal steps occurs primarily thoughelectrochemical action rather than, for example, physical abrasion,sputtering, etc. In some embodiments these steps are performed withlittle or no physical contact with the surface of the workpiece underconstruction at any time. In some cases it has been found useful tocontinue the feature filling process beyond the simple filling of therecesses to a point were raised, inverted, or “embossed” regions arecreated over underlying features. The protecting of the underlyingstructure with excess metal can reduce undercutting, dishing, anderosion as well as the potential adverse impact on the underlyingtopography caused by subsequent device level manufacture and thedielectric planarization steps (e.g., barrier/dielectric CMP). In suchinstances to later remove the overfill, additional removal processsequences may be used, such as a non-contacting wet etch (such as anisotropic wet etch) or membrane mediated electropolishing.

One aspect of the invention pertains to methods of metal depositioncharacterized by the following sequence of operations: (a) causing adeposition accelerator to become attached to a work piece surfaceincluding both recessed and exposed surface regions of the surface; (b)selectively electrochemically removing the deposition accelerator fromthe exposed surface regions without performing substantial metaldeposition on the surface; and (c) after (b) is at least partiallycomplete, depositing metal onto said surface. In such methods thedeposition accelerator remaining attached to the surface increases therate of metal deposition in the recessed regions relative to the rate ofmetal plating in the exposed surface regions. In certain embodiments,the selective electrochemical removal is accomplished by bringing thesurface into close proximity with an electric field-imposing member suchthat the accelerator is selectively removed from the exposed surfaceregions in close proximity with the member and that accelerator moreremote from the member in said recessed regions remains attached. Incertain embodiments, the deposition accelerator is an electroplatingaccelerator. In certain embodiments, operation (b) is performed withoutsubstantial contact with said surface.

Various operations may be performed before removing the depositionaccelerator in (b). Examples of such operations include (1) platingmetal unto said surface to fill at least some of said recessed regions,(2) exposing said surface to an oxide-removing solution.

After operation (b) and prior to operation (c), the method may includecleaning said surface to remove contaminants and/or debris. Suchcleaning may be performed with a cleaning solution. Further, thecleaning may be aided by brushing or megasonic energy.

Another aspect of the invention pertains to methods of removingaccumulated metal forming a constriction at the opening of a recessedregion at the surface of a work piece. Such methods may be characterizedby the following operations: (a) providing a work piece having a surfacewith exposed surface regions and recessed regions, wherein at least someof said recessed regions are characterized by having said constrictionsof accumulated metal; and (b) selectively removing metal constrictionwhile said work piece is electrically polarized without performingsubstantial metal plating on said surface by bringing said surface intoclose proximity with an electric field-imposing member.

Such methods may also include an additional operation, prior tooperation (b), of causing a deposition accelerator to become attached tothe surface including the recessed and exposed surface regions. Then, inoperation (b), the selective removal of constriction metal may alsoremove the deposition accelerator from the exposed surface regions whilesaid work piece is electrically polarized. In certain embodiments, themethod may also include, after operation (b) is at least partiallycomplete, plating metal onto said surface, whereby the depositionaccelerator remaining attached to the surface increases the rate ofmetal plating in said recessed regions relative to the rate of metalplating in the exposed surface regions. Examples of depositionaccelerators include the following: 2-mercaptoethane-sulfonic acid(MESA), 3-mercapto-2-propane sulfonic acid (MPSA),dimercaptoproionylsulfonic acid (DMPSA), dimercaptoethane sulfonic acid(DMESA), 3-mercaptopropionic acid, mercaptopyruvate,3-mercapto-2-butanol, and 1-thioglycerol.

Many of the methods described herein are particularly useful whenapplied to work pieces having at least some of said recessed regionswith aspect ratios of less than one. Further, the invention ispreferably used with work pieces that are partially fabricatedintegrated circuits, such as work pieces in which the recessed regionsinclude trenches and/or vias.

The electric field-imposing member of the apparatus may comprise a flatelectrode, a metallic film or a porous material. The metallic film maybe supported by an flexible substrate. The support may have elasticproperties. The support may be made of, for example, a polymer or ametal. The electric field-imposing member may comprise a membrane,particularly one made of an ion-conducting polymer such as a cationic oranionic membrane.

The electric field-imposing member is usefully brought into closeproximity with the surface, by scanning portions of the surface with themember. The member may be separated from the surface by a film of gas,liquid, or electrolyte. In some embodiments there may be continuous orintermittent contact between the surface and electric field-imposingmember.

Another aspect of the invention pertains to apparatus for selectivelyremoving chemical agents attached to, adhered to and/or adsorbed to thesurface of a planar work piece characterized by recessed regions on saidsurface. The apparatus may be characterized by the following features:(a) an elongated member defining the upper and partial side walls of achamber; (b) an electric field-imposing member defining the lower walland partial side walls of the chamber; (c) an electrode for contactingelectrolyte within the chamber; and (d) at least one contact arm formaintaining electrical contact between the electrode and an exteriorcircuit while said apparatus is moveably mounted on a base.

In certain embodiments, the apparatus also includes a ballast vessel forrelieving exterior pressure imparted on said member to the electrolytein the chamber and a passage communicating between said electrolyte insaid chamber and said ballast vessel. The electric field-imposing membermay include features as set forth above and elsewhere herein.

These and other features and advantages of the invention will bedescribed below in more detail with reference to the associateddrawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graph showing the typical voltage vs. displacementcharacteristics across the interface from the workpiece, through theelectric field supporting electrolyte and the proximity focusingelement.

FIG. 2 is a schematic drawing of the lines of current and voltagecontours at the planar surface and within a recess of a workpiece.

FIGS. 3 a-3 d are schematic diagrams of how metal is deposited with anaccelerator within and around surface features.

FIG. 4 is a diagram of an EFIE accommodating a metal foil PFI accordingto the invention.

FIG. 5 is a diagram of an EFIE accommodating an ion-conducting membranePFI according to the invention.

FIG. 6 is a diagram of an EFIE provided with a pressurerelieving/adjusting system for the internal electrolyte and PFI.

FIG. 7 is a diagram showing the combined use of an anodic and cathodicEFIE according to the invention.

FIG. 8 is a process flow diagram for filling high and how A/R featuresusing SEAR according to the invention.

FIG. 9 shows linear potential sweep response curves of a rotated copperdisk after acceleration dosing for 10 sec.

FIG. 10 shows linear potential sweep response curves of a rotated copperdisk after acceleration dosing for 100 sec.

FIG. 11 is a graph of the expected relationship between acceleratordosing and current density for a particular set of depositionconditions.

FIGS. 12 a-12 c are diagrams sequentially showing high aspect ratiofilling with sub-saturated accelerator dosing.

FIG. 13 is a 3D view of a scanning bar head with lifting apparatus.

FIG. 14 is a 3D view of a device of FIG. 13 mounted for scanning awafer.

DESCRIPTION OF EMBODIMENTS

The invention is directed to a novel plating approach, termed SelectiveElectrochemical Accelerator Removal (SEAR). The SEAR process involvesthe steps of causing an activating, metal-deposition-acceleratingchemical called (also called an “accelerant” or “accelerator”) adeposition (preferably an electroplating) accelerator to become attachedto a surface of a workpiece including recessed and exposed surfaceregions; selectively removing the deposition accelerator from theexposed surface regions by imposing an strong electric field in thevicinity of the substrates surface without simultaneously performingsubstantial metal deposition (e.g. plating) on the surface; and afterremoval of the accelerator is at least partially complete, depositingmetal onto the surface by metal deposition (for example,electrodeposition, electroless deposition, CVD, PECVD, etc.) to lead topreferential deposition of metal in the areas where the platingaccelerator remains (i.e. in the recessed regions). The acceleratorremaining attached to the surface increases the rate of metal depositionin the recessed regions relative to the rate of metal deposition in theexposed surface regions. An electric field imposing electrode is broughtin close proximity to the surface and, due to its proximity, causes theremoval, destruction, or otherwise “deactivation” of the acceleratorfrom the surface. In a particular embodiment, the process may involvecreating a surface wherein an electroplating sensitive accelerator,generally a plating “accelerating” or depolarizing compound, is reactedwith, or otherwise becomes attached to the surface, and the acceleratoris then preferentially removed from raised (non-recessed) regions. Thenelectrodeposition is performed under appropriate conditions for theparticular accelerator chosen (such as bath components and operatingconditions).

The present invention is advantageous over known methods of planarizinga workpiece such as a silicon wafer. Pads and brushes that are used tomake physical contact with a wafer (e.g., with a pad as in CMP, ECMP,Planar Plating, Electroplanarization and SAP) can lead to a number ofundesirable defects including damage to underlying low-K materials.While MMEP, and MMEP with an array of electrodes, may be useful inavoiding physical contact to the wafer, it still planarizes though metalremoval (requiring overburden) and may suffer from a limited ability toplanarize a surface topography due to the operating physics (e.g., asthe topography decreases, the “ohmic difference” mechanism and hence therate of topography reduction decreases), potentially limited compliancelengths of the membrane that is used, and feature edge attack wherebyedges are subject to high removal rate due to field focusing there.

Therefore, the highly selective and often substantially non-contactingmethod according to the present invention for reducing and controllingtopography during deposition that can be combined with non-contactmethods of removal of metal (isotropic surface kinetic controlled dry orwet chemical etching) provides advantages over the prior art. Theinvention is further advantageous since it does not introduce a new setof problems. The invention is useful, for example, in that itfacilitates an electroplating process sequence that 1) is simple andcost effective, 2) creates no new source of defects, 3) fills featuresof all aspect ratios with little, if any, overburden, 4) protects theunderlying structures from dishing or metal loss during metal removal,5) does not physically stress or contact the surface, and 6) mitigatesother problems associated with CMP processing such as erosion and damageto underlying topography.

The method and apparatus disclosed herein solve the problems raisedabove. Furthermore, the method and apparatus disclosed herein solve theproblem of highly variable and difficult-to-control topography commonlyfound as a result of damascene copper electroplating processes. Morespecifically, it enables the “bottom-up” filling of features of allaspect ratios with minimal overburden, enabling controlled (i.e.reduction or tailoring) topography (e.g., planar or “embossing” thesurface over underlying features) without physical abrading or rubbingcontact to the wafer, (e.g., without resorting to the use of a pad orsimilar type of friction/abrading/rubbing element). The invention isparticularly useful in combination with various non-contacting metalremoval techniques, such as isotropic wet etch, electropolishing andmembrane mediated electropolishing. The invention also is useful insimplifying, eliminating or improving the results from chemicalmechanical polishing operations, e.g., elimination of copper chemicalmetal planarization steps and improved dishing and erosion frombarrier/dielectric removal steps.

In a typical embodiment, the process of selectively attaching anactivating or accelerating plating additive (e.g., plating accelerator)is performed in two parts: 1) adsorbing the accelerator onto theworkpiece surface and 2) selectively removing the adsorbed acceleratorfrom the exposed or raised “field” regions. Often the step of adsorbingthe accelerator is preferably substantially uniformly performed over theentire surface of the workpiece, including recesses. In preferred casesthe removal is accomplished without substantially touching or abradingthe surface. In the Selective Electrochemical Accelerator Removal (SEAR)process, the selective removal of the accelerator is accomplished via anelectrochemical operation (e.g., a localized sputtering electrochemicaloxidation or reduction of the raised region of the surface) or a processthat is facilitated by the formation of chemicals created by anelectrochemical process. Other non-electrochemical methods of selectiveremoval may be operable, but less preferred. Also, other non-contactingmethods for selective accelerator removal may be operable, such as forexample, the use of a very rapid pulse of heat emanating from a heatedhead that passes quickly over the surface and can alter, decompose, orotherwise cause the desorption of accelerator from regions of a raisedsurface. The preferred method of removing the accelerator utilizes aelectrochemical techniques and apparatus, which are simpler to enableand have added benefits of better selectivity and control.

Application of the Plating Accelerator

The use of plating accelerators is known in the art. They are typicallyapplied to the workpiece surface by simple contact by spraying orimmersion. In many cases, the presence of the accelerator does notsubstantially interfere with the kinetics of the overall charge transferprocess yet can radically modify the deposition behavior when certainother plating bath additives (e.g. suppressors, halide ions) arepresent. As described in U.S. application Ser. No. 10/739,822, there area number of ways to achieve global activation of a metal surface.

The surface can be sprayed with a solution containing the accelerator,deposited by vapor deposition, condensation, sublimination, chemicalvapor deposition, or any number of other suitable means as would beobvious to those skilled in the art. Examples of suitable activatingadditives include mercapto-group containing molecules such as2-mercaptoethane-sulfonic acid (MESA), 3-mercapto-1-propane sulfonicacid (MPSA), dimercaptoproionylsulfonic acid (DMPSA), dimercaptoethanesulfonic acid (DMESA), 3-mercaptopropionic acid, mercaptopyruvate,3-mercapto-2-butanol, and 1-thioglycerol. These and similar acceleratorshave been found to strongly adsorb to a work piece surface such ascopper metal but do not substantially interfere with the overall chargetransfer process of electroplating, particularly in acidic bathscontaining low levels of halides. The plating accelerator will beglobally applied to the surface of the workpiece, including the exposedplaner surface as well as both high aspect and low aspect ratio recessessuch as trenches and vias.

Elements of the Apparatus for Selectively Removing Plating Accelerator

In general, when the Electric-Field-Imposing Element (EFIE) thatcontains a Proximity Focusing Interface (PFI) is brought in closeproximity to the workpiece and a large potential is applied between theworkpiece and the PFI, the selective removal, destruction, or conversionof the accelerator to an inactive form is selectively achieve. Forexample, to selectively and preferentially remove the platingaccelerator, the method of the invention (SEAR) employs anElectric-Field-Imposing-Element (EFIE) that contains aProximity-Focusing Interface (PFI) that is brought very close to theworkpiece, the proximity being similar to and of the same order or scaleof the topography present on the workpiece surface. In some cases thesome or all portions of the PFI may be brought in contact(intermittently or continuously) with the workpiece surface, which canallows the PFI to register its distance from the exposed regions of theworkpiece surface. The EFIE/PFI hardware has the properties of beingcapable of creating, imposing or causing to induce a spatially selectiveelectrochemical reaction at the workpiece surface. The electrochemicalreaction or reactions associated with EFIE occur preferentially atlocations physically closer to the EFIE focusing interface than atlocations further away from the EFIE focusing interface. Referring toFIG. 1, the electrochemical reaction associated with the EFIE andoccurring at the workpiece surface is induced by the proximity andnearly constant potential of the PFI surface that is typicallytransmitted though a very high resistance electrolyte 22. The termelectrolyte is somewhat different that typically used, becauseelectrolyte often implies dissolved disassociate paired ion ofsignificant conductivity. The electrolyte in this invention is aresistive fluid which often has very few, if any, paired ions able tocarry current in the absence of the imposed high electric field betweenthe workpiece and the PFI. The PFI however can cause the high resistanceelectrolyte to break down and generate charge carriers by decompositionof the fluid at the workpiece surface. These charge carries may beunpaired within a space charge containment region between the PFI andthe workpiece, as in a plasma. This very high resistance electrolyte 22is interposed between the workpiece 21 and the PFI 14. This highresistance electrolyte is referred to as theElectric-Field-Supporting-Electrolyte (EFSE). The EFSE can also servethe purpose of forming a hydrodynamic fluid interface between theworkpiece and PFI so that there is no direct contact of the PFI with theworkpiece and providing lubricity to the workpiece surface as the EFItraverse or is otherwise transported over the surface. The spatiallyselective removal, modification, destruction or other mean of“deactivation” of the accelerator is selectively achieved over thesurface by the spatially specific action of the EFIE proximity focusinginterface combined with the high resistivity EFSE. The EFIE proximityfocusing interface, when combined with the highly resistive EFSE, issubstantially an equipotential surface on the scale at least as large asfeatures of the workpiece features and EFIE/workpiece spacing. Whenbrought very close to the surface, electrochemical reactions arefacilitated to occur preferentially in workpiece areas closest to theEFIE proximity-focusing surface (PFI), and occur at significantly slowerrates or not at all at regions further away from the interface.

By employing a power supply to impose a voltage between the terminalleads of the workpiece and the EFIE (either directly or indirectly tothe EFIE proximity focusing element), and because the conductivity ofthe metal on the workpiece and the system resistance to the EFIEproximity focusing elements surface are much smaller than that acrossthe EFSE, a large electric field is created within and across the EFSE.Hence, a large field can be created over a very small distance and inthe vicinity of the workpiece surface. Referring to FIG. 1, the voltage40 also varies in strength primarily in the direction of the vectordrawn between the workpiece surface and the PFI. Referring to FIG. 2,current (vertical lines 42) passes in a direction substantiallyperpendicular to the gradient in voltage (horizontal lines 41). Thefield strength diminishes as the separation between the elements changesand hence electrochemical reaction rates vary depending on the depth orlocal separation between the PFI and the workpiece. In some cases, aseries of modification of the metal surface occurs as a result of theimposed electric fields and these modifications result in significantlydifferent rate of reaction beyond those expected by similar ohmicconsiderations. For example, when using deionized water as a EFSE with acopper surface, copper may be oxidized at both raise and recessedregions. A parallel reaction of the oxidation of water to form protons(acid) and oxygen, which will occur preferentially at the exposedsurface, can react with the metal oxide, changing the pH locally anddissolve the metal oxide. This selective removal of oxide may results ina significantly increased rate of removal of metal (a non-linearbehavior) and facility the selective removal of any accelerant attachedthereupon.

Electric Field Supporting Electrolyte (EFSE)

Because the ionic conductivity of theelectric-field-supporting-electrolyte (EFSE) is always quite small theterm “electrolyte” as used herein is further explained. Theelectric-field-supporting-electrolyte is a highly resistive fluid,containing none, or only a relatively small concentration of ionicspecies. In some cases the electrolyte is simply a solvent (preferablynon-flammable) such as ultra-pure water (de-ionized water),supercritical carbon dioxide, or ammonia. Organic solvents such aspropylene carbonate, ethylene carbonate, dimethylcarbonate, diethlyenecarbonate may also be used. Gasses can also be used, though they requirelarger imposed electric fields. Suitable gasses include hydrogen,helium, argon, oxygen, BF₄, SF₆, and gas mixtures. Water is found to beparticularly useful because of its low cost, environmental friendlinessand high abundance, but certain conditions may make the use of othermaterials/solvents also desirable. The concentration of ionic species(or ionic complexes) in the EFSE is generally less than 10⁻²moles/liter, more generally less than 10⁻³ moles/liter. The resistanceof the EFSE electrolyte is typically less than 1 microohm cm, preferablyless than 0.1 megaohm-cm. The average electric field imposed between theworkpiece and the EFIE and across the EFSE is quite large, for examplegreater than 5×10⁵ volts/cm. As a specific example, the average distancebetween the EFIE and some “raised” portions of the workpiece closest tothe EFIE may be less than 500 Å and the voltage between the workpieceand the EFIE surface may be greater than 6 Volts. In this example then,the electric field strength is 1.2×10⁷ volts/cm. This exceeds thebreakdown voltage of most solvents, and under such large fields thesolvent of most electrolytes will decompose, and so it is expected thatin many cases solvent breakdown is expected to occur concurrently andmay even aid in the SEAR process. As noted above, for example, in thecase of the use of water and when the workpiece is anodically polarized,oxygen may be formed along with the formation or protons and this mayaid the removal of the accelerator and/or the removal of the metal ontowhich the accelerator is attached (e.g., by avoiding the formation of aresistive metal oxide and changing the pH to acidic conditions locally).

The Electric Field Imposing Element (EFIE) and Proximity FocusingInterface (PFI)

The Electric Field Imposing Element (EFIE) may be, for example, a singleelement or material (in which case the proximity focusing interface andthe electric field imposing element are one and the same). But in othercases, the EFIE may contain multiple elements making theproximity-focusing interface (PFI) more useful. Therefore, the EFIE maybe composed of a number of sub elements or components, one of which isthe PFI.

The PFI may be a solid, a liquid, a gel, or a polymer (including anionic conducting polymer). The EFIE PFI may be an electrical conductor,such as a metal. Alternatively, the PFI may be an ionic conductor (e.g.a cationic membrane). Still further, the PFI may be porous on amicroscopic scale, being resistive to, but still allowing flow undersufficiently high pressure, where the bulk transport of both liquidsolvent and current carrying ions contained therein can be moved.Alternatively, the proximity focusing interface may be nanoporous(allowing or rejecting flow of certain sized molecules and/or ions on amolecular scale) such as typically employed in reverse osmoticoperations.

In another particularly preferred embodiment, the proximity focusinginterface comprises a solid ionic conducting polymer, such as an anionicor cationic conductive and/or selective membranes (e.g., Nafion™available from DuPont Corporation). The EFIE PFI may also be a materialthat is both an electrical and ionic conductor, such as an electrolytefilled electrically conductive material (e.g., nano-metal foam or carbonaerogel).

Examples of EFIE materials and constructions include 1) a flat,electrically conductive electrode (e.g., a polished-flat solidelectrical current collection anode or cathode constructed of metal); 2)a metallic surface film or coating on a very flat, smooth, or polishedinsulator (e.g., a film coating on a smooth, polished piece of siliconor silicon wafer); 3) an electrode formed from a thin metal film orfoil; 4) a thin metal film coated on an plastic or elastic substrates(e.g., a metal film on a rubber or polymer, such as Mylar); 5) a solidpiece or film of porous, non-conductive inorganic or inorganic material(e.g.) polymer filled and containing an electrolyte within its pores(e.g., porous “fitted” silica glass, silica aerogel,resorcinolformaldehyde derived organic aerogel); or 6) a cationic oranionic conductive membrane (e.g., Nafion™, by Dupont). Specificexamples of a liquid EFIE include ion-contain, ion-conductiveelectrolytes substantially immiscible with the underlying EFSE or liquidmetals (e.g., mercury).

In a preferred embodiment, a thin film EFIE (e.g., thin metal film,metal coated film on an elastomer or polymer, a cationic and anionicmembranes, or films of aerogel) is constrained along its periphery, andpressurized on one side. See FIGS. 4 and 5. The membrane or filmdeflects toward the membrane to create a proximity-focusing element,whose face closest to the workpiece is the proximity-focusing interface.The proximity-focusing element is inflated (“blown-up” like a balloon)by having a pressurized fluid on the non-EFSE side of the EFIE. This isfound to be helpful in achieving compliance of the EFIE over longerlengths and, when combined with relative movement between the workpieceand the EFIE and induced EFSE flow in the gap between them and controlthe spacing between the working and counter electrodes. Alternatively,an elastic element (preferably porous when ions must move through it inthe case of using a ion carrying membranes) can be used behind the EFIEwhich is deformed along with the EFIE when it is brought in closeproximity to and traversed near the substrate interface.

In some embodiments, the surface of the EFIE will not substantially orsignificantly follow the topography of the surfaces on the scale atwhich accelerator is desired to be selective removed. Rather, thesurface of the EFIE may span the recessed regions rather than steppingto follow the workpiece topography thereby making the separation betweenthe EFIE and the workpiece surface within the recess larger than it isbetween the EFIE and the raised regions or general surface. Theproperties of the EFIE combined with the compressibility properties andflow characteristics of the EFSE and operating conditions may need to beconsidered to achieve this. While the EFIE is flexible in someembodiments and therefore may substantially deform and penetrate intothe recessed regions under conditions under which the workpiece and theEFIE are not moving with one another, the relative motion, theincompressibility of the pressurized fluid and viscous flow forces (whenusing liquid EFSE) and pressure of the assembly can enable the EFIE totraverse or “fly” over recessed regions of considerable size and lowaspect ratio. In other cases the EFIE may actually touch the surface,either continuously, periodically, or intermittently. The spacingbetween the EFIE and the workpiece can also be controlled and maintainedas described in U.S. Pat. No. 6,756,307 and PCT Application No. WO2005/042810 in the names of Mazur et al., both of which are incorporatedherein by reference.

In some embodiments, the EFIE may be porous to the macroscopic flow ofeither the EFSE or electrolyte contained in or behind the porouselectrode. In certain embodiments, the EFIE should support conditions ofcreating a proximity focusing element and interface that has a highlyequipotential surface facing the workpiece. The resistance of the powersupply lead or the counter electrode to the proximity focusing interfaceis typically much smaller than (usually 1% or less) than that across theelectric-field-supporting-electrolyte (EFSE). This may be achieved byusing EFIE proximity focusing elements having high electricalconductivity (as in a metal or semiconductor) or having a highlyconductive ionic solution or ion transport material between the counterelectrode and the proximity-focusing interface. In the latter case, theproximity-focusing interface is removed or remote to the electrochemicalpairing reaction, being located spatially away from theproximity-focusing interface (for example, when using a cationicmembrane). This creates a “virtual electrode” at the EFIE front surfacethat may be in the form of a solid member or body that contains asurface that faces the working electrode and exhibits a substantiallyconstant (equipotential) voltage and acts in a physical manner as if afaradaic electrode was in the same given location,

In cases where a membrane PFI is used, the front surface of a membraneproximity focusing element at its interface is substantially held at anear-constant voltage because of the relative resistances of the system.The voltage gradient changes abruptly and becomes nearly constant beyondthe proximity focusing interface, as shown in FIG. 1. A schematic of thevoltage and current profiles between the workpiece and proximityfocusing interface, and around a recessed and raised region is presentedin FIG. 2. Areas where lines of current are depicted closer together areregions of higher current density.

Method of Electrochemical Selective Removal of Plating Accelerator

While the term removal in describing the SEAR process has been used, itis understood that it is not necessarily required for the accelerator tobe physically removed from the surface to achieve the goals of theinvention or to practice this invention. For example, the acceleratormay be simply altered (e.g. decomposed, oxidized, reduced, or otherwisemodified). The accelerator may be driven into or buried underneath adeposit during the process (e.g., by metal electrodeposition orion-bombardment). But regardless of the manner in which it isaccomplished, the chemical functionality of the accelerator as anaccelerating compound is diminished or eliminated by the SEAR processthrough the presence and action of the EFIE.

SEAR differs from the prior art in part, because it involves thepreferential or selective removal of a chemically active orelectrochemically active compound globally attached or adhering to anexposed workpiece surface by any one of many techniques, includingelectrochemical techniques. The chemically active material has theproperties such that (1) due to its presence and in location where it isbound; and (2) when combined with other materials and processes, it hasa reduced inhibition to deposition. In the case of electro-deposition,the deposition is accelerated or is less polarized in the regions wherethe molecules of chemical active material are present. The strength ofthe bond of the accelerating molecule with the surface must besufficiently strong such that surface diffusion of the molecule is slowwith respect to the time over which selective removal and plating occur,and the accelerating molecule must not become substantially incorporatedor otherwise loose its accelerating characteristics during thedeposition process.

Plating of Metal after Accelerator is Selectively Removed

Generally, any deposition process known in the art may be used.According to the present invention, the plating deposits metalpreferentially into recessed regions of a workpiece without requiringspecial controls to balance the rates of additive deposition andremoval. The conditions for filling low aspect ratio and high aspectratio features are, however, often different, and in many cases areperformed in separate operations, using different materials, equipmentand steps. But the invention may be practiced without continuallycontacting or otherwise modifying the workpiece surface during thevarious steps of depositing the layers on the workpiece. Use of aphysical contacting device at any point in the process is not requiredin many embodiments of the invention. The process of the invention isadvantageously fast and can lead to excellent contrast between therelative deposition rate within the initially recessed features and thefield areas.

Embodiments of Workpiece Processing using SEAR

The invention is useful in achieving filling of features of both highand low aspect ratio features. While the general SEAR procedures forfilling these two classes of features are similar, the specificoperating conditions and flows can be slightly different, so these arein one case disclosed as separate embodiments. However, in manyembodiments of the invention, the features are filled sequentially,filling high aspect ratio features first, and then filling low aspectratio features on the same workpiece. In other embodiments only highaspect ratio features are filled by SEAR technology, and, for example,standard electrodeposition “overplating” is performed to fill low aspectratio features. Finally, in other embodiments, high aspect ratiofeatures are filled by classical methods, and the SEAR process is usedonly to selectively fill low aspect ratios.

High Aspect Ratio Feature (Features Deeper than Wide) Filling

Prior to applying the steps of SEAR for high aspect ratio features, theworkpiece is first optionally pretreated. Examples of pretreatmentinclude applying a reducing agent to remove surface oxides, depositing ametal seed layer (liquid atomic layer deposition or electrolessdeposition), or simply application of a wetting agent. A preferredmethod of selective high aspect ratio feature filling begins with thestep of treating the surface with accelerator by chemical exposure ofthe surface (e.g., by spraying with a solution) or exposure of thesurface to an electrolytic solution that is used to electrochemicallyform an accelerator on the surface. For example, one can 1) spray asurface with a water solution containing the chemical mercaptopropane-or mercaptoethane sulphonic acid (chemical treatment method) or 2)cathodically polarize (applying a reducing potential and current to) aworkpiece in a bath containing an electrochemically active accelerator.The resultant structure is schematically shown in FIG. 3 a. Metal atoms11 (which often starts as a metal seeding layer) with attachedaccelerator molecules 13 and dielectric substrate 18 are shown. In FIG.3 d the workpiece 10, PFI 14 and EFIE 15 are schematically shown. Themetal atom 11, metal ion 12 and accelerator molecule 13 symbols arecommon to FIGS. 3 a-3 d. The electrochemically active accelerator is, inmany cases, a compound that can be transformed into a chemically activeaccelerator, such as a dimer of an accelerating compound (e.g.dimercaptopropane sulphonic acid or dimercaptoethane sulphonic acid).This transformation of the accelerator often occurs by anelectrochemical reduction process performed with or without simultaneousmetal electrodeposition. For example, in the case of electrochemicalactivation, the electrolyte may also contain other materials such asmetal ions (e.g., copper), a suppressor, chloride ion and levelercompounds useful in the deposition of metal and the conversion of theaccelerator to a surface chemically active form, and metal depositionmay occur concurrently with accelerator deposition. As a specificexample, as electrochemical current is passed, it is believed that adimer such as dimercaptopropane sulphonic acid is reduced to the monomermercaptopropane sulphonic acid, and becomes then strongly attached tothe surface. The concentration of accelerant used in this step isgenerally quite low, for example 2-50 ppm of mercaptopropane sulphonicacid or dimercaptopropane sulphonic acid (MPSA and DMPSA). The chemicalor electrochemical treatment typically takes from about 2 to 30 seconds.Currents (when applicable) are from 0.5 to 5 mA/cm². The concentrationsused are generally much lower than those suitable to fill low aspectratio features discussed below, because the process relies on a surfacearea reducing mechanism and the concentration of accelerator during thefeature filling process to achieve its goal.

Referring to FIGS. 9-11, exemplary results of testing of sub-saturatedaccelerator “surface dosing” are shown. Before each test, a copperrotating disk was first cleaned and polished by performingelectropolishing in a 85% phosphoric acid solution, as known in the art(see, for example, U.S. Pat. No. 5,096,550 naming Mayer et al. asauthors). This process is seen to both removes any adsorbed acceleratordeposited on the surface from previous experiments and produces areproducibly smooth surface as demonstrated by the fact that itreproducibly creates curves, and, without dosing, indicates the completeabsence of adsorbed accelerator. Next, the electrode is immersed whilerotating at 300 rpm into a solution of predetermined acceleratorconcentration for a predetermine time (thereby “dosing” the surface withthe accelerator). Immediately after this process, the surface is rinsedwith a spray of fresh deionized water. The rinsing effectivelyterminates the potential for any further accelerator adsorption byeliminating its supply. FIGS. 9 and 10 show linear potential sweepresponse curves of a rotating copper disk (electrode area ˜0.7 cm²)after 3-mercaptopropane sulphonic acid accelerator dosing at 10 sec and100 sec, respectively. Accelerator dosing with other known platingaccelerators showed similar behavior, though the times, concentrations,saturation conditions and voltammetry (changes in polarization) differedsomewhat. The electrolyte used in FIG. 9 contained 175 g/L sulfuricacid, 17.5 g/L copper ion, 1000 ppm Basf Pluronic™ L-62 polyethlyeneglycol (as a plating bath suppressor), and 50 ppm chloride ion. Thebehavior is not specific to this particular bath formulation (acidconcentration, metal concentration, suppressor concentration ormolecules) or metal (e.g. silver, gold, nickel show similar behavior).Generally, the particular chloride concentration is paired with theparticular type of suppressor being used, though its requiredconcentration tends to be less than about 100 ppm to be effective. Thecounter electrode is a sheet of copper foil, and the rotation rate wasset to 100 rpm. The potential is swept to progressively more negativevalues from its open circuit value of approximately −0.4V vs. Hg/HgSO₄at 20 mV/sec and the current response recorded. These and other results(e.g. varying the rotation rate vs. dosing operation) demonstrate theability to modify the polarization behavior and tailor the amount ofadsorbed accelerator between zero and its saturated value by varying theconcentration of accelerator in the dosing solution, the time ofexposure, and the mass transport convection conditions (e.g. rotationrate). The trends show that at relatively low concentration and shortertimes (10 ppm and 10 seconds for MPSA) yield only a small amount ofacceleration, but at high time and concentrations (estimated for MPSA aswhen the product of the exposure time and concentration exceeds about5000 ppm*sec) yields a saturated condition. The saturation value mayrepresent complete monoloyer coverage of accelerator film, or some otherthermodynamic limit.

FIG. 11 schematically illustrates the expected relationship betweenaccelerator dosing and fractional acceleration (related to localdeposition rate, or current density) for a particular depositioncondition (e.g. accelerator molecule, electrodeposition voltage,temperature, CVD chamber pressure, etc.). The y axis, termed thefractional acceleration, “f”, is a measure of the local relative amountof accelerated deposition (related to the depolarization forelectrodeposition) of a surface. It is relative to the extremes of noacceleration (slowest possible deposition rate) and saturated or maximumacceleration (fastest possible deposition rate). Its value typicallytherefore varies between a value of zero and one. Fractionalacceleration can be a function of many parameters, but for thisdiscussion with all other parameters fixed, is related to the amount ofaccelerator (surface concentration or accelerator dosing exposure), “A”,at a point on the surface. In general, fractional acceleration will alsobe a function of the composition and condition used for the deposition(e.g. acid concentration, metal ion concentration, suppressor type andconcentration, temperature, applied potential, etc), though generallyonly a weak function of time unless the accelerator is forcibly removed,destroyed, or geometrically concentrated or dispersed. In the case ofdeposition by electrodeposition, fractional acceleration, “f”, and canbe determined for a particular set of operating condition by therelationship

${f = \frac{\left( {i_{acc} - i} \right)}{\left( {i_{acc} - i_{\sup}} \right)}},$

where I_(acc) is the metal deposition current density (or depositionrate) with a saturated or nearly saturated surface concentration ofadsorbed accelerator, i_(sup) is the current density (or depositionrate) of a surface deposited under the exact same conditions except withno adsorbed accelerator, and i is the current density (or depositionrate) of the surface with some intermediate concentration of surfaceaccelerant concentration or exposure between these two extreme limits.The accelerator surface concentration that corresponds to the currentdensity i may change in time at a particular point on the surface bygeometric concentration (reduction or increases in local surface). Thiswill change its local value of f, and hence is corresponding depositionrate. Alternatively, the concentration of acceleration can change byfirst being saturated (by directly chemical exposure and having acorresponding local value of unity for J), and then creating asub-saturated concentration a SEAR or SMMART process. As can be seen inthe figure, points on the curve where small changes in concentrationlead to large changes in acceleration rate (e.g. low values offractional acceleration and dosing in this figure) are desired whenusing geometric concentration effects are desired (such as filling highaspect ratio features). It is believed that if the concentration is toohigh, geometric concentration of accelerator will not lead to anysignificant change in polarization or further increase in fractionalacceleration or deposition rate (flat portion of the f vs. A curve athigher values of A). For SAP, SEAR and SMMART processes, starting with asaturated concentration leads to the recessed feature filling being atthe highest possible rate. Then, if all or nearly all accelerator can beremoved from the field, the contrast in deposition rate between thelocations where the accelerator has been removed (the field) and withinthe feature is achieved. The authors not, however, that there are a fewcases which this general principle of saturating a surface withaccelerator to achieve maximum contrast in deposition rate is violated.Specifically, when removal of accelerator from a sub-saturated surfaceis easier or more complete than from a saturated surface, and/or theresultant difference in plating rates achieved between regions ofapplied and un-removed accelerator and removed accelerator are greaterif using a less than saturated concentration, then a sub-saturatedcondition may be useful.

The surface concentration in FIG. 11 is at an optimal desired surfacestate 80 on the field and raised regions after accelerator removal. Thenext part 81 of the isopotential acceleration curve indicates the rangeof the desirable state within a high aspect ratio feature during fill.The portion 82 of the curve is the range of the undesirable state forlow aspect ratio feature fill. Finally, The portion 83 of the curveindicates the desired surface concentration prior to accelerator removalfrom the field for low aspect ratio feature fill. If we assume 1) that auniform concentration of surface adsorbed accelerator is deposited onthe surface and in a field, 2) if the surface concentration ofaccelerator is such that an increase in concentration will lead to afurther depolarization of the surface for the deposition process, and 3)that the accelerators surface diffusion is much slower than the rate andtime for the deposition process, then as a feature grows, its localsurface area will decrease its local polarization will also decrease,resulting in an increasing rate of deposition. Therefore, under theseconditions, plating will initially occur more rapidly at the featuresbottom corners (FIG. 12 a). Later, the features corners meet, and thefeature begins to growth from the bottom upwards (FIG. 12 b). As it doesso, the feature continues to collect accelerator from the side-walls(FIG. 12 c), increasing the surface concentration and resulting in acontinuously decreasing polarization, until either the concentrationbecomes saturated or the rate of change with further increase inaccelerator becomes negligible. The critical element in achieving thishigh aspect ratio filling process is setting the appropriatepreconditions for the process, namely a concentration of accelerator ata significant sub-saturated level, and not allowing the deposition rateat the upper wall surface being to high so as to close the feature offbefore the metal fills from the bottom. Therefore, prior to initiatingand for achieving optimal filling, the upper section of the cavityshould 1) have a side wall structure that is slightly open or vertical(but not constricted or necked, which might lead to the formation of afill choke-point) and 2) the concentration of accelerator shoulddecrease from the bottom of the feature to the opening, ideally with theconcentration being zero near the top and on the field. Examples of howto achieve these goals using this invention are now presented.

The data of FIGS. 9 and 10 are derived from flat surfaces. Depending onthe concentration of the accelerator or accelerator precursor and otheroperating conditions (e.g. current, flow, temperature, etc.), it isbelieved that the rate at which accelerant become attached may result inpreferential concentration at the exposed field regions and less in therestricted areas. This is potentially the opposite of the desiredconfiguration useful in filling the features, as noted above. In othercases it may be possible to achieve substantially more uniform surfaceconcentrations, but generally the surface concentration at these earlystages will likely be lower on the surfaces inside the feature due toits limited accessibility to the accelerator source from the solution.Only later in the process, when metal is deposited (initiallyisotropically) over the surface and geometric concentration ofaccelerator on that surface can occur, can one achieve higherconcentrations within the recessed regions, as shown in FIGS. 12 a-c.The metal atom and accelerator molecule symbols in the figures are thesame as those used in FIG. 3 d. However, if one selectively removes someor all of the accelerator from the field/raised-surface after theaccelerator has been deposited over the whole surface, an improvement inthe relative rates of plating within the features can be achieved asshown in FIG. 3 b. Selective removal is achieved by using the methoddescribed herein where the electrochemical action occurs preferentiallyin regions near the exposed surface (field), with little or no removalof accelerator or metal inside the feature.

As another embodiment, a surface may be electrochemically plated (e.g.0.5 to 30 seconds, 0.5 to 5 mA/cm², 0.25-150 coulombs charge) in a bathcontaining 10 to 100 ppm dimercaptopropane sulphonic acid, 10 to 80 g/Lcopper sulfate, 10 to 200 g/L sulfuric acid and 100 to 1000 ppm L-92polyetheylene oxide suppressor. These ranges are for illustrativepurposes only as other combinations and ranges are possible.Alternatively the surface may be treated with 2-50 ppm mercaptopropanesulphonic acid for from 2 to 30 seconds. After either of theseoperations (or one followed by the other) the surface is completelyrinsed of electrolyte with deionized water. See FIG. 3 b. Next, SEAR isperformed on the surface. High resistivity water is applied over thesurface, the surface is rotated or otherwise passes under the EFIE, theunit is anodically polarized (or alternatively cathodically polarized)and electric current is passed between the workpiece and the EFIE.

When anodic polarization is used, some metal on the substrate may beconcurrently removed with the accelerator. As an additive benefit, suchmetal removal may be performed preferentially at the top opening (theneck) of a feature in order to remove undesirable accumulated metal thatoften limits the ability to fill extremely deep features. Hence, if aprocess that is previously used to deposit metal (such as PVD seeding ofthe surface) yields a constricted or necked feature opening, anodicpolarization using the same methods and apparatus for SEAR can also beused to preferentially remove metal there and open up the feature. Thisis graphically represented in FIG. 3 c. This is a “side reaction” orside benefit that may be favorable where it aids in dislodging, or“undercutting” the attachment of the accelerator from the surface.Therefore, quite apart from the use of SEAR to selectively removeaccelerator from exposed planar surfaces, SEAR has an independent use inproviding a method of removing accumulated metal forming a constrictedchoke-point or neck at the opening of a recessed region at the surfaceof a workpiece. Generally, this comprises the steps of (a) providing aworkpiece having a surface with exposed surface regions and recessedregions, wherein at least some of the recessed regions are characterizedby necks of accumulated metal; (b) causing a plating accelerator tobecome attached to the surface including said recessed and exposedsurface regions; and (c) selectively removing the plating acceleratorfrom the exposed surface regions while the workpiece is electricallypolarized without performing substantial metal plating on the surfacewhereby metal forming the necks is also preferentially removed. Thisgeneral method of removing accumulated metal may be then be optionallyfollowed by the step d) after step (c) is at least partially complete,plating metal onto the surface, whereby the plating acceleratorremaining attached to the surface increases the rate of metal plating inthe recessed regions relative to the rate of metal plating in theexposed surface regions.

In further describing this process the solvent (e.g. water) decomposes,and some current associated with this additional side reaction is alsoconsumed. The formation of acid (protons) may help to decrease the pH atthe surface and improve the solubility of the metal (rather than, forexample, having it form a metal oxide). The fraction of currentassociated with the side reactions (not directly associated withfaradaic charge transfer to the accelerator itself) can be large,approaching 100%. However, the amount of material removed is generallyvery small. As little as 10 to 100 A appears to be sufficient in manycases to remove almost all the accelerant from the surface. In somecases essentially no metal removal is required. Removing too much metalat this point in the process where there is often very little metalcovering the surface makes control and minimization of the removalimportant. Charges from 20 to 200 mC/cm² are found useful. In many casesas little as 10 mC/cm² are less can be used. The voltages applied acrossthe EFSE may range from 3 to 20V, generally 5 to 10 V are useful.Current or voltage pulsing (on/off, reversing direction, etc.) may beapplied as desired, and may enable better process control in someoperations.

After removing the accelerator from the field areas using the SEAR asdescribed above, the wafer is typically placed into an electrolyticplating solution. In preferred embodiments the electrolyte containsmetal ions, a suppressor, chloride ion, and an acid, optionally aleveler, but little or no accelerator (either electrochemically activeor chemically active). Small amount of accelerator and levelercompounds, when used, primarily serve the function of controlling thesurface texture (e.g. increasing the surface brightness by reducingmicro-roughness as well is mitigating the formation of any growthprotrusion), changing the grain orientation and size, and incorporatingdesirable impurities that aid in the annealing process. The process iscontinued until the features are filled. Filling is superior to aprocess in which the SEAR step is not performed because a much largerdifference between the concentration of accelerator in the feature tothat on the field or near the feature opening is achievable.

Filling Low Aspect Ratio Features

Filling of low aspect ratio features (features wider than deep) proceedsusing some similar approaches as for high aspect ratio features.However, generally it is desirable to contact, adhere to, and/or reactwith a much higher concentration of accelerator to the surface beforeselectively removing it from high field areas using SEAR. Because thefeatures are wider than they are deep, geometric concentration ofaccelerator does not appreciably occur in this process and thereforethat process (geometric concentration) does not significantly lead toselective filling. The process proceeds primarily by creating differentrelative amounts of plating accelerator at the recessed regions and thefield regions, which remains largely unchanged throughout the fillingprocess. Therefore, creating a saturated or near saturated acceleratorconcentration is desirable. For example, a higher concentration of DMPSAshould be used and a larger current density applied to achieve a highconcentration of surface accelerating monomer from the electrochemicalconversion (reduction) of the dimer. For example, 50 to 500 ppm DMPSAand current densities of greater than 5 mA/cm² for 5 to 20 seconds areuseful. Alternatively, direct chemical adsorption of MPSA from anaqueous solution at concentrations of 50 to 2000 ppm for 2 to 10 secondsare also effective. After application of the accelerator, the surfaceshould be completely and thoroughly rinsed, and removal of theaccelerator performed from the exposed field regions using SEAR proceedsin a similar manner to that for high aspect ratio features. For usespecifically on low A/R features, a stiffer, less flexible and lesscompliant EFIE PFI may be desirable to maintain the spacing between thebottom of features and the PFI, because the distance between the edgesof the feature are larger and penetration or dishing into the feature isexpect to be greater. Different operating conditions (higher velocitiesbetween the workpiece and the PFI and higher electrolyte flow rates) maybe desirable. It is desirable to maintain electrode spacing and hencecontrast between the removal of accelerator from the recessed regionsand field regions. However, control of the amount of metal removed fromthe field is often less critical than during high aspect ratio filling.Metal deposited on the field during the high aspect ratio featurefilling process increases the amount of metal that can be removed fromthe field areas before all field metal is removed from some locations.Also, preferential removal at the mouth/edge of the feature is lesslikely to improve the process, because closure of the very wide featuredoes not occur as it can in very narrow, high aspect ratio features.Some metal removal or decomposition of the metal can be expected and maybe advantageous when anodic removal of the accelerator is the method ofoperation. In cathodic reduction SEAR, the workpiece is cathodicallypolarized and formation of dissolved molecular hydrogen (as dissolvedgas) is a typical side reaction and product.

Embodiments of Hardware Configurations of the EFIE

In particularly preferred embodiments of the hardware, referring to FIG.4, the EFIE proximity focusing interface 14 comprises a metal foil 20 aor plastic film coated with a metal film, creating a PFI membrane. Thefoil, forming a chamber 23 with upper and side walls of the EFIE isinflated with fluid (gas or liquid) on the opposite side of the foilfrom the proximity focusing interface and workpiece 10, workpiece metalsurface 21 electrolyte (EFSE) 22. The composition of the metal filmshould resist corrosion by materials used in the operation. Examples ofsuitable materials for the metal film include noble metals (Pt, Pd, Ir,Au) and other electrochemically stable materials (Ru, carbon, mercury).A chamber containing the inflating fluid is selectively pressurized toestablish membrane rigidity and control. The membrane is pressurized andbrought in close proximity to the surface while the surface is wettedwith high resistance electrolyte (EFSE) and while the workpiece is movedunder the membrane. The relative speed of the workpiece and membrane istypically 5 to 100 cm/sec, more specifically 10 to 50 cm/sec when usingwater as an EFSE. A power supply connected to the workpiece and EFIE(for example, by an electrical contact at the workpiece periphery and ametal film membrane) is energized, imposing a voltage between the twoelectrodes and allowing current to pass. One should avoid physicalcontact of the metal film with the workpiece, because if it does touch,direct electronic current (as opposed to ionic current) will passbetween the workpiece and the film, and reduce or stop the removal ofthe accelerator. If contact occurs, polarization of the EFSE is reducedand the removal efficiency is diminished. Also, electronic arcing oreven welding of the surfaces might occur, so in use, the metal foil PFIspatial separation must be maintained. The membrane can be moved overthe surface as required to achieve selective removal of the accelerator.As noted above, some metal removal and solvent breakdown products mayform concurrently with the process of removing the accelerator. If metalis deposited onto the PFI from the workpiece, periodic removal of thatmetal can be accomplished by periodically etching the deposited metalfrom the PFI interface. In the case of deposited copper on a Pt foilmembrane, a number of suitable etchants may be used, such as a mixtureof hydrogen peroxide and sulfuric acid, or nitric acid. Alternatively,any deposited metal may be removed by reversing the current direction todeposit the metal onto the workpiece or onto a sacrificial body. Whileother materials can also be used for the PFI or as an etchant tofacilitate removing metal deposited on the PFI, when metal from thesubstrate is deposited on the EFIE, use a noble or suitable materialthat allow the metal to be subsequently removed without effecting theEFIE base material (for example, by chemical etching or anodicoxidation) is a useful attribute.

In another embodiment, the proximity-focusing element is an ionicconductor membrane, preferably an anion conducting membrane, exemplifiedin FIG. 5. The methods and processes using an ionic conducting membrane20 b are referred to herein as Selective Membrane Mediated AcceleratorRemoval Technology (SMMART). It has the advantage over the use ofelectronically conductive metal PFIs (20 a) in that intermittent orstray physical contact of the membrane does not cause electricalshorting of the current to the workpiece, but the disadvantage thatphysical contact is more likely to lead to abrasion of the membrane,leaving a debris on the wafer. The front surface of the membrane(closest to the substrate) acts as a virtual counter electrode proximityfocusing interface 14. Though it is believed that a faradaic processdoes not occur there, the potential is maintained at a nearly constantvalue and the interface can be brought very close to the surface. Metaldeposition and gas evolution are avoided by having the auxiliary counterelectrode spatially removed from the interface, and hence can beconstructed as to not interfere with the operation. Longevity of theoperation without maintenance can therefore be achieved. Therefore, theionic conductor is chosen so it does not conduct electricity andfaradaic reduction processes do not occur on its interface. A counterelectrode 24 then resides in a chamber 23 on the opposite side of theion conductor from the workpiece. The chamber 23 is formed by themembrane 20 b and the upper and side walls of the EFIE. A highconductivity electrolytic solution resides in chamber 23 on the counterelectrode side of the assembly. The conductivity of this electrolyte istypically at least 100, more typically 10,000, times more conductivethan the electric field supporting electrolyte 22 (EFSE). Examples ofsuitable electrolytes are water-based solutions containing substantialconcentrations of acids, bases, and inorganic or organic salts(e.g. >2%/wt solutions). The function of the electrolyte is to carry theionic current from the ionic membrane to the counter electrode. Anelectrolyte fill inlet 27 and outlet 26 are provided to allowelectrolyte to circulate within, and to fill and empty, chamber 23.Referring to FIG. 6, the inlet and outlet 27, 26 may be connected to aclosed system for relieving and adjusting the pressure exerted by thefoil or membrane 20 on the workpiece metal surface 21. The systemcomprises a ballast chamber 28 useful in quickly adjusting the internalpressure of the membrane chamber 23 and an appropriate valved flow meter30, pressure sensor 29, pump 31 and reservoir 32. The ballast vessel 28will typically at least partially contain a gas to accommodateexpansion, or alternatively, is open to the atmosphere, and allows fluidto rapidly move in and out of the chamber without substantial changes ininter-chamber pressure. The system may be adjusted to maintain apredetermined constant force at the membrane-workpiece interface so thatan optimum field is maintained without exerting undue force to possiblydamage the membrane or workpiece surface topography or impede itsprogress across the workpiece The power supply electrical leads, 25 aand 25 b (FIG. 5), respectively, are connected to the counter electrode24 and the workpiece metal surface 21. In an embodiment, the proximityfocusing element is composed of a cationic conducting film held at itsperiphery and is an “inflatable membrane” similar to that discussed forthe metal foil membrane above. A particular example of a useful cationicmembrane material is Nafion™, manufactured by Dupont. During SMMARTanodic workpiece-polarized operations, positive charged speciesgenerated at the workpiece (e.g. protons, metal ions from workpiecemetal, positive charged ionic forms of the accelerator detached from thesurface) migrate to the membrane interface and through the membrane.Charge balance requires that an equivalent faradaic reaction occur atthe counter electrode, housed in the EFIE electrolyte chamber. Forexample, if the highly conductive solution contains metal ions and acid,hydrogen gas and/or metal plating would be expected at the counterelectrode. In the case of cathodically workpiece-polarized SMMARToperations, the counter electrode is preferably a noble or dimensionallystable electrode (e.g. Pt, Ta, Au) and the high conductivity electrolyteshould be substantially devoid of any metal ions (e.g. a high purityacid solution). In this case, the particular accelerator must beoperable to be removed from the surface by a reduction process. If thereduced accelerator species is neutral, then it is removed by beingdissolved in the flowing electric field supporting electrolyte. If thereduced accelerator species created by a cathodic SMMART process isnegatively charged, an anionic conductive membrane would be preferred.

Apparatus

FIGS. 13 and 14 show a preferred configuration of the SEAR/SMMARTapparatus useful for performing linear sweeps or scans over a wafersurface. A linear scanning bar head assembly 201 containing anelectrolyte inlet 202 and outlet port 203, a counter electrodeconnection terminal 204, and proximity focusing interface 205 (forexample, a inflated and supported Nafion membrane) can be swept over awafer (not shown) in a linear sweeping motion. The head assembly can belifted and dropped via a pneumatic cylinder 206 which can be used tocontrol the applied down force between the membrane/wafer interface, ordrive the head assembly to a metered hard stop position using a gapthickness control adjusting assembly 207. The front to back alignment ofthe head to the wafer and the angle of attack or camber of the head isadjusted by camber and alignment adjusting screws 208. A six axis forceand torque sensitive load cell 209 is used to monitor the alignment andfrictional forces during processing. The head assembly is mounted to aposition controlled motorized linear slide mechanism 210 which is heldto the equipment using a gantry 211 having a linear motor-driven slide214. A vacuum chuck 212 allows the placement and flat mounting of thewafer below the scanning head, and can be rotated during or betweenlinear scans of the head, for spray application of etchant, accelerator,rinse water, or other desirable components. Above the head locatedazimuthally off axis from the direction of mechanical sweep of the headare two or more electrical contacts 213 that can be articulated. Theelectrical contact makes electrical contract to one end of the waferperiphery while the scanning bar assembly 201 is passing over the otherend of the wafer. After passing though approximately the wafer center,one of the contacts is raised to allow the head to base under itslightly after the other contact is lowered. In this way, continuouselectrical contact is maintained with the wafer throughout the waferscan.

The apparatus described in this section has certain inherent advantages.Among these is the fact that all the various operations described hereinand laid out in FIG. 8 can be performed within this single station ormodule, thereby increasing the throughput and eliminating the timeneeded to move the workpiece between various station designed to performa sub-set of these processes. The workpiece can first be processed toremove neck metal of high aspect ratio features in the apparatus using ahigh resistance electrolyte, a cationic membrane, and the scanning barover the wafer.

Prior to, or after removing neck metal, one may apply a cleaning etch,perform various rinsing steps, and apply the accelerator (e.g. eachusing a spray nozzle), Then (if not performed concurrently with neckopening) the accelerator can be selectively removed from the field andupper regions of high aspect ratio features by anodically polarizing thesurface and passing a cationic membrane over the surface in a sweepingmotion and performing SMMART, with deionized water as the EFSE. In anyof the bar head sweeping operation, multiple passes or sweeps can bemade, with rotation of the wafer between sweeps. This approach is foundto improve the uniformity of the processes and the removal/depositionoperation. Afterward, one can fill features in the same apparatus bychanging the electrolyte that resides between the heads PFI (thecationic membrane in this example) from water to a high conductivitymetal-ion-containing electrolyte containing appropriate platingadditives. The polarity of the head is reversed (the workpiece is nowmade cathodic), resulting in preferential deposition of metal into highaspect ratio features. Because low aspect ratio feature may not beselectively accelerated or filled at this point, the sequence cancontinue by rinsing off high conductivity electrolyte form the surface,performing or repeating the steps of cleaning, etching the surface,removing oxides, rinsing, and globally applying accelerant (again,performed, for example, by spraying the surface with the appropriatesolutions). Then, one can repeat anodic selective accelerator removal(e.g. using deionized wafer as the EFSE) to create a high concentrationof accelerator inside low aspect ratio feature and removing acceleratorselectively from the exposed or raised field. The conditions forperforming this selective accelerator removal may be different than thatof the prior, high aspect ratio filling operation. Finally, a highconductivity metal plating electrolyte with appropriate additives can beapplied to the surface between the cationic membrane and the workpiece,the workpiece cathodically polarized, and the bar head scanned over thesurface, thereby plating metal preferentially into low aspect ratiofeatures. The wafer can then have excess overburden metal removed usinga metal etch chemistry. As one can see, a large number of operations arethereby accomplishing, all one station/module, ultimately creating awafer with metal filled features having a vast range of widths, and verylittle metal if any metal left in undesirable area's (e.g. the field).

Post SEAR Feature Filling

As mentioned above, after performing SEAR, metal deposition (e.g.electrodeposition) can be performed preferentially in the recessedregions of the workpiece surface. In a particular example of this, MPSAis sprayed from a solution onto a workpiece. The workpiece is thenrinsed to remove residual accelerant from the surface, and then SEAR isperformed (e.g. by SMMART). Next, the workpiece is electroplated using aplating solution containing metal ions and an appropriate suppressor forMPSA (e.g. polyethylene oxide or polyethylene glycol or co-polymers ofthese, with ppm concentrations of chloride ion). Some additional acid isalso often used to enhance the conductivity of the electrolyte. Platingcathodic current is applied to the workpiece and the recessed featuresare filled with metal preferentially (i.e. bottom up filling). In oneembodiment of the invention, the filling of the features continues to apoint where the amount of metal in the features is sufficient for thehigh and low aspect ratio recessed features to be completely filled, andthen is continued to create an embossed structure (raised or protrudedmetal above the thickness of the field) over all recessed features. Thisis a unique capability of this process that enables protruded metal tobe deposited over low aspect ratio features, and it has been found thatit can be highly advantageous when properly controlled. After plating,the workpiece is rinsed of residual plating solution and dried (e.g. ina spin rinse dryer). In some embodiments the workpiece is then annealed(200-450° C., 0.5 to 30 minutes). Removal of metal from the surface isthen performed. However, because of the reduced topography and raised(protruded or embossed) structures enabled by SEAR, removal techniquesother than costly CMP or eCMP can be performed. For example, anisotropic wet etch, electropolish or membrane-mediated electropolish canbe performed. The process is typically terminated when the metal in thefield clears. If excess filling (embossing) of metal over the featureswas performed during the SEAR and plating processes, the first pointthat all metal clears to the dielectric plane occurs at regions devoidof recessed features, but metal remains over all the features. Inclassical process flows, metal clears first at low aspect ratio featuresand around their periphery. Hence, the embossing can “protect” damascenefeatures and changes the order of clearing typically seen in classicalprocess flows (e.g standard electroplating and CMP) improving the finaltopography and yield significantly.

While in many cases application of current to the workpiece is made byphysically contacting the surface metal with a metallic lead at theperiphery (a contact connecting it to the power supply), an alternative,“indirect” or electrochemical contacting method may also be used. Anexample of use of an indirect contacting method is described in U.S.Pat. No. 6,143,155. Referring to FIG. 7, two or more SMMART EFIE's canbe used simultaneously to supply indirect current to the surface. OneEFIE 50 will be anodically polarized with respect to the workpiece andaccommodate an anode 24 a. Another EFIE 51 will be cathodicallypolarized with respect to the workpiece and accommodate a cathode 24 b.Oxidative and reductive faradaic reactions then occur under the PFIs 20b at the workpiece surface 21, generating or consuming electrons.Electrons (electrical current) then passes though the workpiece to theopposite SMMART EFIE.

In a particular preferred apparatus embodiment, the operations ofapplying accelerator, rinsing the wafer, SEAR (e.g. SMMART), featurefilling and metal removal are combined on one piece of hardware.Referring to FIG. 8, a workpiece such as a wafer is provided 301,typically oriented face up and held on a chuck (e.g. a vacuum chuck). Atthis point SEAR may be used in a step 302 to accomplish, as previouslydescribed, simultaneous reduction or removal of any metal neck regions,usually present around high A/R features, and to prepare the surface forhigh A/R filling. However, this step may be optionally omitted and thehigh A/R features may be filled in step 303 without preparation by SEAR.

After filling the high A/R features, the surface of the wafer isoptional cleaned in step 304 with a cleaning solution to remove anycontaminants from the filling step, such as surface residual acceleratoror leveler. For this purpose an etchant is preferred that oxidizes aportion of the metal to a metal oxide (e.g., copper oxide). This step istypically followed by or is performed simultaneously with a step ofremoval of the metal oxide 305 from the surface of the substrate using ametal oxide complexing or etching agent. For step 305 any suitableoxidizing agent capable of forming copper oxide may be used, however, itis generally preferred that a self-limiting oxidation process be used.That is, the oxidation of the copper occurs slowly and controllably.Exemplary oxidizing agents include, for example, dilute aqueoussolutions of peroxides (such as hydrogen peroxide), persulfates, ozoneand/or permanganates. In some embodiments, the oxidizing solution has arelatively high pH, e.g., at least about 5. In more specific cases, thesolution has a pH of between about 5 and 12, and in even more specificcases, between about 6 and 10. To control the oxidizing solution pH, aneutralizing agent may be used, preferably one with an anion that doesnot complex with copper ions. Examples include tetra-alkyl ammonium andalkali metal salts of hydroxides. The oxidizing etch solution may alsocontain a complexing agent that complexes with the copper to control theetching rate of the acid, and/or a surfactant to further modulate theetch rate.

Once copper oxide is formed by the oxidizing solution, it can be removedby using any suitable copper oxide etchant in step 305. In someembodiments the copper oxide etchant selectively removes copper oxidewithout substantially attacking the copper crystallites or grainboundaries. Suitable copper oxide etchants include dilute acids andacids with high pKa values, EDTA, ammonia, glycine and various coppercomplexing agents, for example. Exemplary acids include dissociatedinorganic acids such as phosphoric acid, sulfuric acid and organic acidssuch as acetic acid. Appropriate pH for the etching solution istypically in the range of about 0 and 2. Suitable complexing agents mayinclude ethylenediamine tetraacetic acid (EDTA), glycine, citric acidand salts thereof, maleic acid and salts thereof, and certain ammoniumcompounds known to those of skill in the art, for example. In someembodiments, separate oxidizing and oxide etching solutions areemployed. In other embodiments, a single solution is used for bothoxidizing copper and removing copper oxide. By controlling the ratio ofcopper oxidizing agent and copper oxide etchant in such solutions, onecan control the amount of oxidation and depth of the intermediate copperoxide film that is formed on the surface of the substrate. Preferredetching solutions are described in the US patent application by Koos et.al. In a preferred embodiment, the solution includes between about 0.05%and 15% glycine (or copper complexing agent) by weight and between about0.5% and 20% peroxide (e.g., H₂O₂) by weight. In a specific embodiment,for example, an etching solution containing about 1% (by weight) glycineand about 3% (by weight) H₂O₂ is used. Preferably, the single solutionincludes a buffering agent that maintains the pH at a specific value.Buffering agents such as acetate, carbonate, or phosphate can beselected depending on the desired pH value. More specifically, thesolution may have a pH of between about 5 and 12, and in even morespecific cases, between about 6 and 10. Alternatively, the naturalbuffering characteristic of the glycine (pH around 9). The pH can beadjusted by the addition of an appropriate agent such as an alkali metalor tetra-alkyl ammonium hydroxide.

The etching and/or oxidizing solution may additionally contain acorrosion inhibitor to minimize grain attacks and surface roughening ofthe exposed copper metal. Suitable corrosion inhibitors include, but arenot limited to, benotriazole (BTA), thiourea, certain mercaptans, andimidazoles. Note that in addition to or instead of adding corrosioninhibitor to the etching solution, the substrate surface may be treatedwith a solution containing corrosion inhibitor prior to etching.

After these pre-SEAR cleaning steps, the wafer is typically sprayed instep 306 with a solution containing accelerant. Next the wafer isusually rinsed (e.g. with water). Next accelerant is selectively removedin step 307 by electrochemical action by use of SEAR (e.g. using aSMMART removal head and process). Then the wafer is optionally cleanedagain in step 308 to remove any residuals particles, for example, byrandom abrasion with the membrane. The cleaning solution, in thisinstance preferably are relatively strong, low pH acids such as HCl, HFor sulfuric acid. A solution of 5%-100% sulfuric acid is useful. Acommercial cleaning agent from EKC under the trade name CMP-5500 is alsouseful for this purpose. Mechanical or ultra- or megasonic agitation canalso be used to aid in the cleaning and particle removal process.

The wafer is then plated to fill low A/R features in step 309, using abath primarily containing metal ions and a suppressor, as describedabove. A conventional immersion-bath wafer plating apparatus, a thinfilm microplater, or a scanning proximity focusing plating head can beemployed. During the plating the wafer becomes wetted with electrolyteprimarily containing metal ions and a suppressing compound, with otherelements as optional as described above. If the operations of SEAR areto be repeated, rinsing to remove the plating electrolyte should beperformed, optionally the surface should be etched and cleaned, andaccelerator reapplied as above. Upon termination of filling 310 thefeatures, the surface may be annealed in step 311, using, for example,hot reducing gas and/or IR heating. An inert atmosphere “dome”containing reducing gas may be placed over the wafer, and annealing canbe performed without moving the wafer from the processing module. Afteroptionally annealing the workpiece, overburden metal can also be removed312 in this same module by a wet etching process, as described in, forexample, Controlini and Mayer, or Koos et. al. Alternatively, metal canbe removed using a scanning membrane mediated electropolishing head, asdescribed by Mazur. Then according to conventional wafer processes thebarrier layer may be removed in step 313 and planarization processes 314may be applied. Alternatively, the barrier can be removed using abarrier selective wet etch, such as a hot alkaline solution to remove W,Ti, TiN, Ta, or TaN from a surface with embedded copper. For example, a30%/wt solution of potassium hydroxide at 80° C. will remove thesebarrier materials and leave copper within the damascene trenches. As canbe seen by this process flow, a number of processes that previouslyrequired a number of separate stations can now be combined into onemodule/station, substantially increasing productivity.

The following example is presented only for illustrative purposes and isnot intended to limit the scope of the invention in any way.

EXAMPLE

The procedure to achieve these results is now described, but we are notimplying that this is the only procedure or the optimal procedure. A 200mm wafer was first sprayed with deionized wafer to wet the surface for 3seconds, then sprayed with a 5% solution of sulfuric acid for 5 secondsto remove a surface oxide, followed by rinsing with a spray of DI waterto remove the acid, followed by spraying with a solution containing 1g/L MPSA in water for 10 seconds to uniformly accelerated the wafer. Thewafer was then rinsed completely with water and then dried in air byspinning the wafer at 1500 rpm at about 20C.°. (Despite rinsing anddrying, the accelerant still remains attached to the surface). Next aSMMART EFIE head was passed over the surface at 50 cm/sec. The velocitywas maintained constant by varying the rotation rate as a function ofradial position of the head. Pure deionized water was used as anelectric field supporting electrolyte. An approximately one molarsolution of sulfuric acid was contained in the counter electrode chamber(i.e. used as the high conductivity electrolyte). A Nafion™ cationicmembrane was used as the proximity focusing elements. The voltagebetween the counter electrode inside the EFIE assembly and the wafersurface potential was 9 volts vs. the counter electrode, and was pulsedat a cycle of 1 ms on, and for 4 ms off. The SMMART head was scannedover the surface once, covering about 65% of the total wafer surface(from a radius of about 1 cm to 8 cm from the center, surface areaprocessed about 200 cm²). The approximate surface area of exposurebetween the SMMART membrane and the wafer surface at any instant in timewas about 3 cm² (as determined by the region of metal removal in aseparate experiment). The total charge passed during the process wasapproximately 10 C. Based on mass difference measurement, approximately50% of this charge (5 C) was associated with the removal of copperoriginally at the surface. The average thickness of metal removed isestimated to be less than 90 Å without any attempt to optimize theoperating conditions to achieve uniform removal, such as maintaining thehead over a particular region of the wafer for the same length of time.It is believed that the balance of charge (5 C) was used in oxidizingwater and the accelerator. After removal of the accelerator, the waferwas plated in a plating bath containing 18 g/L copper ion, 180 g/Lsulfuric acid, 50 ppm chloride ion, and 1000 ppm L-62 PEO suppressor. Aconstant plating current of 5 amps was applied for 60 seconds. Therelative rate of plating in the recessed feature regions (widths rangingfrom 5 to 100 um wide and 0.5 um deep) was about 8 times greater than inthe field areas where the accelerator had been preferentially removed.

Those skilled in the art may make numerous uses and modifications of thespecific embodiments described, without departing from the inventiveconcepts. The steps recited may, in some instances, be performed in adifferent order; or equivalent structures and processes may besubstituted for the described structures and processes. The invention isto be construed as encompassing every novel feature and novelcombination of features present in or inherent to the methods andstructures described in the following claims and their equivalents.

What is claimed is:
 1. An apparatus comprising: a wafer holderconfigured to hold a wafer, the wafer including field regions andrecessed features; an electric field-imposing member; a controllerconfigured to: (a) cause a deposition accelerator to become selectivelyattached to surfaces of the recessed features including: (i) causing thedeposition accelerator to become attached to the field regions of thewafer and the surfaces of the recessed features of the wafer; and (ii)causing selective removal of deposition accelerator from field regionsin close proximity to the electric field-imposing member to a greaterextent than any corresponding accelerator removal from surfaces of therecessed features more remote from the electric field-imposing memberthan said field regions, the selective removal comprising anelectrochemical process that is performed without performing substantialmetal deposition onto the field regions and surfaces of the recessedfeatures; and (b) after (a) is at least partially complete, cause thedepositing of a metal onto the field regions and the surfaces of therecessed features, wherein the deposition accelerator remaining attachedto the surfaces of the recessed features increases the rate of metaldeposition onto the surfaces of the recessed features relative to therate of metal deposition onto the field regions, and wherein the metaldeposition continues until the recessed features are filled and themetal is protruding in regions of the recessed features relative to thefield regions.
 2. The apparatus of claim 1, further comprising: achamber configured to hold an electrolyte, the chamber comprising anelongated member which defines the upper and partial side walls of thechamber, wherein the electric field-imposing member defines the lowerwall and partial side walls of the chamber; an electrode positioned tobe in contact with the electrolyte when the electrolyte is providedwithin the chamber; and at least one contact arm for maintainingelectrical contact between the electrode and an exterior circuit whilethe chamber is moveably mounted on a base.
 3. The apparatus of claim 2,further comprising a ballast vessel for relieving exterior pressureimparted on said electric field-imposing member to said electrolyte insaid chamber and a passage communicating between said electrolyte insaid chamber and said ballast vessel.
 4. The apparatus of claim 2,wherein said electric field-imposing member comprises a flat electrode.5. The apparatus of claim 2, wherein said electric field-imposing membercomprises a metallic film.
 6. The apparatus of claim 5, wherein saidelectric field-imposing member further comprises an elastic substrateaccommodating said film.
 7. The apparatus of claim 2, wherein saidelectric field-imposing member comprises a porous material.
 8. Theapparatus of claim 2, wherein said electric field-imposing membercomprises a membrane.
 9. The apparatus of claim 8, wherein said membranecomprises an ion-conducting polymer.
 10. The apparatus of claim 1,further comprising one or more spray nozzles, wherein the controller isfurther configured to cause the one or more spray nozzles to spray asolution comprising the deposition accelerator onto the surface of thewafer held in the wafer holder.
 11. The apparatus of claim 1, whereinsaid electric field-imposing member comprises a flat electrode.
 12. Theapparatus of claim 1, wherein said electric field-imposing membercomprises a metallic film.
 13. The apparatus of claim 12, wherein saidelectric field-imposing member further comprises an elastic substrateaccommodating said film.
 14. The apparatus of claim 1, wherein saidelectric field-imposing member comprises a porous material.
 15. Theapparatus of claim 1, wherein said electric field-imposing membercomprises a membrane.
 16. The apparatus of claim 15, wherein saidmembrane comprises an ion-conducting polymer.